This invention relates to an electrically heated blanket, and more particularly, to a blanket to warm a human body by heating the blanket by electrifying a heater wire laid in the blanket.
The blanket referred to in this invention means every kind of blankets to warm human body including a blanket used as a bedcover, a blanket which directly covers a human body, a blanket which is spread over a bed or a mat on which a human body is laid, and so forth, irrespective of a fabric composing the blanket.
In the past, a bad effect of a magnetic field and an electric field on human body was a problem in this kind of blankets. To solve the problem, a couple of means are suggested.
One of the means is to de-energize magnetism by making synthetic resin of insulating material, which covers the heater wire, contain a special material, and the other means is to de-energize magnetism by offsetting magnetism by laying two heater cables adjacently and in parallel to each other in each of which heater wire electricity flows in opposite directions.
It was proved recently that the latter means works more effectively to de-energize magnetism in comparison to the former.
The bad effect of magnetism almost became able to be avoided due to the above-mentioned means for solution, however, as the heater wire is conventionally arranged all over the blanket, an effect of remaining magnet on the head of human being is worried about.
In addition, the heater wire is so constructed that temperature can be controlled by an equipped controller. The heater wire is laid all over the blanket.
However, a trunk of a human body has comparatively high temperature by nature. Therefore, when the heater wire is heated, the temperature of a portion of a blanket, which covers a chest of the body, rises sooner than a portion of the blanket, which covers feet. Consequently, heating of the chest caused perspiration and the temperature of the head rose because of circulation of heated blood to the head, which presented a problem of sleep disturbance.
An object of the present invention is to lessen an effect of magnetism on a human head and to control rise of temperature of a portion of a blanket covering near a human chest.
In order to achieve the above-mentioned object, the electrically heated blanket according to this invention is structured to be able to control temperature by a controller. The electrically heated blanket comprises a main blanket body, and two heater cables arranged over the main blanket body to form a space of a concave or a U-letter configuration in a plan view, said two heater cables being arranged adjacent in parallel to each other and their beginning ends being connected to the controller and their terminal ends being connected to each other so as to flow electric current therein in opposite directions.
In the present invention, each of the two heater cables preferably comprises a first heater wire which is wound helically around a core thread, a second heater wire which is wound concentrically with, around periphery of and in the same direction with the first heater wire via an insulating layer, a sensor wire which is wound concentrically with and around periphery of the second heater wire via an insulating layer, and an insulating layer covering the sensor wire.
Further, in the present invention, when the main blanket body is of large size, the two heater cables are preferably arranged so that the if heater cables form another space of a concave or a U-letter configuration in a plan view in continuous with the first space at the upper portion of the main blanket body.
Further, the fabric composing the main blanket body is preferably undergone antibacterial treatment.
According to this invention, the two heater cables are arranged over the main blanket body so that the heater cables form a space of a concave or a U-letter configuration in a plan view at the upper portion of the main blanket body. Because of the arrangement, magnetism can be de-energized (99%) by the electric current flowing in opposite directions, and heating vis-a-vis the chest, having a high temperature by nature, can be controlled, by which uncomfortableness caused by heating of the chest and the head can be eliminated and the effect of the remaining magnetism (about 1%) on the chest and the head can be avoided in advance.
Thus, over-perspiration can be controlled and comfortable sleep can be obtained.
Furthermore, by making the two heater cables wind concentrically with each other, the heater cables can be positioned adjacently to each other and the effect of de-energizing of magnetism can be intensified. In addition, by arranging the sensor wire on the very surface, which means there exists two insulating layers in total, leak of remaining magnetism can be prevented more surely. At the same time, by arranging the sensor wire on the very surface, it becomes easier to sensor the temperature of the main blanket body, and control of the temperature can be done accurately.
Still further, according to this invention, in a main blanket body of a larger size like a queen size or a king size, said effect of de-energizing of magnetism and the control on heating the chest can be obtained for two human bodies at the same time by arranging the two heater cables so that the heater cables form another space of concave or U-letter configuration in a plan view in continuous with the first space at the upper portion of the main blanket body.
The other advantages of this invention will be fully understood from the following description on embodiments on reference to the drawings.